Solution-processed blue/deep blue and white phosphorescent organic light emitting diodes (PhOLEDs) hosted by a polysiloxane derivative with pendant mCP (1, 3-bis(9-carbazolyl)benzene)

The synthesis and characterization is reported of an efficient polysiloxane derivative containing the 1,3-bis(9-carbazolyl)benzene (mCP) moiety as a pendant unit on the polysiloxane backbone. In comparison with mCP, the mCP-polysiloxane hybrid (PmCPSi) has significantly improved thermal and morphological stabilities with a high decomposition temperature (Td = 523 °C) and glass transition temperature (Tg = 194 °C). The silicon–oxygen linkage of PmCPSi prevents intermolecular π-stacking and ensures a high triplet energy level (ET = 3.0 eV). Using PmCPSi as a host, blue phosphorescent organic light emitting devices (PhOLEDs) effectively confine triplet excitons, with efficient energy transfer to the guest emitter and a relatively low turn-on voltage of 5.8 V. A maximum external quantum efficiency of 9.24% and maximum current efficiency of 18.93 cd/A are obtained. These values are higher than for directly analogous poly(vinylcarbazole) (PVK) based devices (6.76%, 12.29 cd/A). Good color stability over a range of operating voltages is observed. A two-component “warm-white” device with a maximum current efficiency of 10.4 cd/A is obtained using a blend of blue and orange phosphorescent emitters as dopants in PmCPSi host. These results demonstrate that well-designed polysiloxane derivatives are highly efficient hosts suitable for low-cost solution-processed PhOLEDs

Recent advances in polymer organic light-emitting diode (PLED) using non-conjugated polymers as the emitting layer and contrasting them with conjugated counterparts

Polymer organic light-emitting diode (PLED) is one of the most studied subjects in flexible electronics thanks to their economical wet fabrication procedure for enhanced price advantage of the product device. In order to optimize PLED efficiency, correlating the polymer structure with the device performance is essential. An important question for the researchers in this field is whether the polymer backbone is conjugated or not affects the device performance. In this review, recent advances in non-conjugated polymers employed as the emitting layer in PLED devices are first discussed, followed by their contrast with the conjugated counterparts in terms of polymer synthesis, sample quality, physical properties and device performances. Such comparison between conjugated and non-conjugated polymers for PLED applications is rarely attempted and hence this review shall provide a useful insight of emitting polymers employed in PLEDs.Publisher PDFPeer reviewe

Phosphorescent Organic Light-Emitting Devices: Working Principle and Iridium Based Emitter Materials

Even though organic light-emitting device (OLED) technology has evolved to a point where it is now an important competitor to liquid crystal displays (LCDs), further scientific efforts devoted to the design, engineering and fabrication of OLEDs are required for complete commercialization of this technology. Along these lines, the present work reviews the essentials of OLED technology putting special focus on the general working principle of single and multilayer OLEDs, fluorescent and phosphorescent emitter materials as well as transfer processes in host materials doped with phosphorescent dyes. Moreover, as a prototypical example of phosphorescent emitter materials, a brief discussion of homo- and heteroleptic iridium(III) complexes is enclosed concentrating on their synthesis, photophysical properties and approaches for realizing iridium based phosphorescent polymers

New charge-transport materials for OLED applications

Novel fluorene-1 ,3,4-oxadiazole and spirobifluorene-1 ,3,4-oxadiazole compounds 202 and 211, respectively, have been synthesised. Compound 202 was blended with MEHPPV in various ratios and incorporated into organic light-emitting diodes (OLEDs).The devices were found to emit light purely from MEH-PPV up to very high doping levels. When the device architecture ITO/PEDOT:PSS/MEH-PPV :202/Ca:Al was used it was found that increasing the amount of202 increases the lifetime of the device. Novel bipolar fluorene- I ,3 ,4-oxadiazole-triphenylamine molecules 237 and 240 were synthesised using silicon protecting groups. When incorporated into devices with architecture ITO/PEDOT:PSS/237 or 240/Ca:Al it was found that the materials facilitated the transport of electrons and holes as well as acting as blue-green emitters with efficiencies of up to 0.26%/0.6 cd A-1. Compound 237 also performed well when blended with MEH-PPV giving rise to efficiencies two orders of magnitude greater than for pure MEH -PPV devices

Light-Emitting Devices – Luminescence from Low-Dimensional Nanostructures

[no abstract available

Iridium complex, a phosphorescent light-emitting diode material, serves as a novel chemical probe for imaging hypoxic tumor tissues

Iridium complex, a promising organic light-emitting diode for next generation television displays, emits phosphorescence. Phosphorescence is quenched by oxygen. We used this oxygen-quenching feature for imaging tumor hypoxia. Red light-emitting iridium complex Ir(btp)~2~(acac) (BTP) presented hypoxia-dependent light emission in culture cell lines, whose intensity was in parallel with HIF-1[alpha] expression. BTP was further applied to imaging five tumors (four from human origin and one from mouse origin) transplanted in athymic mice. All tumors presented a bright BTP-emitting image even 5 min after the injection. The BTP-dependent tumor image peaked at 1 to 2 h after the injection, and was then cleared from tumors within 24 h. The minimal BTP image recognition size was 3 to 4 mm in diameter. Compared with ^18^F-FDG/PET images, BTP delineated a clearer image for a tumor profile. We suggest that iridium complex has a vast potential for imaging hypoxic lesions such as tumor tissues

Amorphous Metal-Free Organic Phosphors for Sensor Applications

Phosphorescent organic light-emitting diodes are promising for many applications such as display and solid-state lighting because they can reach 100% theoretical internal quantum efficiency. In order to realize bright purely organic phosphors, efficiently promoting intersystem crossing from singlet to triplet and suppressing vibrational dissipation of triplets must be achieved. In this dissertation, I systematically investigated the two critical processes and devised some strategies to achieve bright room temperature purely organic phosphorescence in amorphous films and optical ozone sensors based on phosphorescence phenomena. Embedding organic phosphors into amorphous glassy polymer was investigated as the first strategy to efficiently suppress the triplet vibration by restricting molecular motion of the embedded organic phosphors. This system showed temperature dependent phosphorescence attributed to changing vibrational characteristics of the matrix polymer. An optical temperature sensor integrated in a microfluidic device was devised and demonstrated. Incorporating strong hydrogen bonding between a newly devised purely organic phosphor and hydrogen bonding capable matrix polymer was the second strategy, resulting in much brighter phosphorescence. Modulation of hydrogen bonding by water showed unique reversible phosphorescence-to-fluorescence switching behavior, which was utilized to develop a ratiometric water sensor. Based on the finding that the phosphorescence intensity of the purely organic phosphors is sensitive to environmental ozone concentration, I revealed that the origin of the ozone sensitivity is oxidation of the aldehyde moiety of the organic phosphors and devised highly sensitive and convenient optical ozone sensors by utilizing the observed inverse linear correlation between the phosphorescence emission intensity and the ozone concentration. Since manipulating conjugation length of organic phosphors is a powerful tool to tune the emission color, establishing an understanding on the conjugation length effects on the phosphorescent emission intensity is important. The effects of the conjugation length of the purely organic phosphors on their phosphorescence intensity were systematically studied using a combined experimental and computational approach. The obtained knowledge regarding the role of intermolecular interactions for vibration suppression was adapted to achieve high thermal conductivity in amorphous polymers by designing hydrogen bonding donating and accepting polymer pairs, providing uniformly distributed strong interpolymer linkage, and leading to high thermal conductivity of 1.5 Wm-1K-1.PHDMacromolecular Science and EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/111449/1/dongwook_1.pd